Method of copper sweetening



June l2, 1945. H. E. MEssMoRE ETAL 2,378,092

I METHOD OF COPPER SWEETENING mm x25 A n.23". 02.522 A Y Patented June 12,y 1945 corr i METHOD COPPER. SWEETENING Harold E. Messlnore, Bartlesville, Okla.; and James M. Mason, Chicago, Ill., assignors to Phillips Petroleum Com Delaware pany, a corporation of Application september 1o, 1943,*seria1No. 501,876

comms. (c1. 19e- 30) This invention relates to the sweetening of gasoline and other petroleum oils, and more particularly it relates to an improved processof carryiug out a sweetening operation. i Specifically, the invention relates to improvements in the sweetening of petroleum oils by the cupric chloride method shown in Schulze et al., U. S. 1i964,-

y 219,and in Henry et al., U. S. 2,089,373.

In the sweetening of sour petroleum -distillates by the so-called liquid copper sweetening process, the sour oil containing sulfur in the form of f time of contact in such a mixing mal-odorousmercaptans is intimatelyand vigorously contactey '.with an aqueous `solution vof a cupric salt, usw ly cupricchloride (and may be made from cupric sulfate and a soluble chloride, as sodium chloride). The mixture of the copper chloride treating solution and the oil is then a1- lowed to settle and separate, whereupon the sweetened upper oil layer is removed from the lower aqueous layer. Uusally the sweetened gaso oline is next contacted witha stabilizing agent such as an alkalinesodium sulde solution which treatment serves to remove any traces of Copper compounds and prevents color instability or other deterioration of the product. The copperl sweetening agent is regenerated by blowing with a free oxygen-containing gas such as air, then recirculated for further use. t

Certain extraordinary gasolines or petroleum distillates are slow to sweeten by the conventional Ik copper sweetening method described above.` This is believed to bedue largely to the concentration and type of mercaptan .contained in these oils. Since mercaptans may be termed thoalcohols, there may then be the same types oi mercaptans as alcohols, for example, primary, secondary and tertiary, depending on the number vof replaceable hydrogen atoms remaining attached to the carbon atom to which the mercaptan (-SH) group is attached. It is known that primary mercaptans may be rapidly converted tothe corresponding disuldes by the oxidizing action'of cupric chloride, secondary mercaptans less-rapidly, and tertiary mercaptans relatively slowly, and it is thought that the tertiary mercaptan content may be the cause for the relatively slow sweetening of some gasolines and rpetroleum distillates.

Since hydrocarbon oils and aqueous solutions, such as the copper chloride sweetening solution, are immiscible, itis necessary to' obtain intimate Contact therebetween in yan attempt tovexpedite reaction. At the same time,` too vigorous contacting may result in the formation ofl a relatively stable emulsion. It has been foundvthat mixing of these two immiseible liquids by acentrifugal mixing pump gives suicient vcontactii'tg .in the normal commercial installation. Obviously,l the device is of limited duration.

In the treatment of oils which are abnormally i slow-to sweeten, it has been suggested to use a bypass for recirculation of a portion of the mixing pumpdischarge (intimate mixture of copper chloride solution and oil)' into the sour oil charge line. 'I'his recirculation increases the apparent time of contactingof'the sourcil and the aqueous sweetening agent. At the same time the partially spent treating solution can react with some yeasily convertible mercaptans in the sour oil so thatat the inlet to the mixing pump the oil is actually partially sweetened. Another improvement has been to install a packed tower type contacter so that'the above mentioned bypassed mixtureof partially spent copper treating solution and sweetened oil and sour charge oil may be more intimately mixed bythe time the mixture reaches the mixing pump. In this Ymethodv of operation the new or fully regenerated copper treating solution is added tothis latter mixture just previous to entrance into the mixing pump. y y

We have now further improved lthis methodof sweeteningA by removing substantially all of the fully spent treating solution prior to the addition of the regenerated solution. In this improved operation, to the partially spent treating solution is added the raw, sour gasoline or petroleum distillateto besweetened, wherein the easily oxidized mercaptans are converted into the corresponding disuldes. After this partial sweetening takes place the. resulting spent. solution is rremoved from the partially sweetened oil. Then fully regenerated treating solution is addedwherein this solution of high oxidizing powermay react with the mercaptans which are slower and more dimcult to sweeten.. This improved processpermits the more eflicientuse of the copper chloride treating solution for the sweetening of oils generally considered dicult or slow to sweeten.

The oxidizing or sweetening powerof the copper chloride solution may be measured' by conventional potentiometric methods using a saturated calomel electrode. In commercial practice a vfully aerated and regenerated copper treating solution mayhave an oxidation potentialas high as 4.10-

420 millivolts, abbreviated hereinafter m. v. .A

spent solution of the same copper and chloride content may have an oxidation potential as low as 360 m. v. or at times even lower. If. one volume of spent'treating solution .of 360 m. v.is mixed with one volume of regenerated solutionv of `a2() solution takes place.

m. v., the resulting mixture will possess an oxidation potential of approximately 380 m. v., and not the arithmetic average.

An object of this invention is to improve the copper chloride solution sweetening process.

Another objectof this invention is to improve the copper chloride solution sweetening process in such a manner that oil stocks generally con sidered diiicult to sweeten may be more easily and rapidly sweetened.

Still another object of this invention is to improve the operation of the liquid copper chloride sweetening process wherein the treating solution of low oxidizing power may sweeten the sourness u which is easy to sweeten and the fully regenerated treating solution of high oxidizing power may reac1l with the Sourness which is normally considered difficult to-sweeten.

Still other objects and advantages of our improved process will be apparent to those skilled in the art from a careful study of the following detailed disclosure, in which the gure illustrates diagrammatically one form of apparatus of the present invention by which our improved process may be carried out.

Referring now to the accompanying drawing, a motor driven centrifugal ymixing pump is indicated at I and a separating tank at 2, in which gravity separation of the treated oil and copper Sour oil to be sweetened enters the system by way of a line 3, controlled by a valve 4. Partially spent copper treating solution enters line 3 from line I3, and the mixture of the sour oil with this copper solution passes downward through the packed contacter tube 6. From this contacter this mixture now containing partially sweetened oil and spent treating solution passes by way of line 1 into the separating tank 8, which is similar in construction to the separating tank 2. From tank 8 the upper partially sweetened oil layer leaves by way of line 9, controlled by valve I0, new or fully regenerated copper treating solution enters by line II controlled by valve I2, and the mixture then is taken into the suction side I5 of the centrifugal mixing pump I. In this mixer these two immiscible liquids are thoroughly and eiiiciently contacted and an emulsion-like looking mixture is discharged into the separating tank 2 by way of line I6 controlled by valve I1. In this tank sweetened oil and partially spent treating solution separate as two liquid phases, the oil phase passing from the tank by line I8 controlled by valve I9; while the treating solution ows from the tank by line I3, the flow being controlled by valve 20. As mentioned hereinabove, the partially spent treating solution from tank 2 passes through line. I3 into line 3, thereby. completing the ow cycle of the copper chloride solution.

A bypass line 2l connects the mixing pump discharge line IB with the sour oil line 3, and the liquid iiow therethrough is controlled by valve y.

Fully spent copper treating solution separated from the partially sweetened oil in separating tank 8, is removed vtherefrom by line 23 controlled by valve 24. Line 23 conducts this spent solution to an aeration apparatus, not shown, wherein the spent solution is oxidized or regenerated by atmospheric oxygen. The regenerated solution then re-enters the system through line The packing material 5 in contacter -6 may be essentially any standard material suitable for the purpose at hand. It must, obviously, be inert toward both the oil being treated and the copper chloride treating solution, the latter being slightly acid. The packing material may be arranged in the contacter 6 in essentially any manner desirable to accomplish the result of vbreaking up streamlined flow of the two immiscible liquids and promoting contacting and therefore chemical reaction between them. The diameter and length of the contacter 6 are such as to permit appreciable time contacting so that a large part of the mercaptans easy to react may be converted by the time the oil leaves the contactor.

Separating tanks 2 and 8 are equipped with gauge glasses 25 and 26, respectively, of conventional design, for the purpose of observing the position of the interface between the copper solution and oil layers, represented by numeral 21 in separating tank 8 and numeral 28 in separating tank 2.

In the operation of the sweetening process according to our invention, sour oil to be sweetened enters the system through line 3, the ow being controlled by valve 4. Partially spent copper chloride treating solutionv from line I3 enters line 3 near the latters junction with the contactor column 6. In this contactor column the said copper chloride solution is rather intimately mixed with the sour oil whereby a certain amount of chemical reaction or sweetening occurs. In this sweetening column, we believe that the major portion of the primary mercaptans, mentioned hereinbefore. a much smaller proportion of the secondary mercaptans, and poss ly a very small amount of the slow-to-react ter ry mercaptans are sweetened. Since the primary mercaptans are ordinarily present in oils in far greater proportions than all other types of mercaptans combined, we then believe that a relatively large proportion of the total sweetening actually occurs in this contacting column. The resulting copper treating solution is ordinarily fully spent, especially When treating oils of appreciable sourness.

The mixture of spent treating solution and partially sweetened oil passes from contactor 6 through line 1 into the separating tank 8, wherein the two immiscible liquid phases separate. In this separating tank a high copper solution level as indicated by numeral 21 is carried, the relative amount of treating solution in the tank being much greater than the volume of the partially lsweetened oil. It is not necessary to maintain any exact or definite level, since all that is necessary is to make certain that the copper solution remains in this separating tank 3 sufficiently long that substantially all oil has ample time in which to become separated therefrom. Any oil which is withdrawn with the spent treating solution through line 23 will be lost by evaporation during regeneration, unless provision is made for reclaiming same.

By maintaining a high copper solution level in the separating tank 8, the copper solution residence time is considerably longer than is the residence time of the partially sweetened oil therein. It is not necessary that all traces of copper solution be separated from this partially sweetened oil since the regenerated treating solution is added to this partially sweetened oil while the latter is in transit in line 9. The minute amount of spent copper solution has substantially no detrimental efect upon the relatively large amount of regenerated solution added.

The partially sweetened oil and regenerated copper treating solution from line 9 enter the agsvaoee 3k mixing pump I',- andi become :thoroughly and vigorously mixed wherein it isintended thatthe remaining, slower to sweeten mercaptans, become fully sweetened. The oil-solution mixture upon dischargefrom the mixing pump I has an appearance of a coarse grained emulsion, the oil apparently being the continuous phase and the copper treating .solution the discontinuous phase. This mixture then passes through line. I into the separating tank 2 wherein copper solution and sweetened oil separate. In thistank a very low copper solution level is maintained in order to increase to a maximum the retention kor settling time of the sweetened oil so that the oil leaving said tank by line I8 willcarry no traces of suspended copper treating solution. The settled copper solution may or may not contain traces of oil on account of its relativelyshort retention time in separator 2. Since this partially spent treating solution is recycled through line I3 to line 3 where sour oil is contacted, it is immaterial whether or not this solution carries oil', and in case it does, we have found it to be very small in amount. 3 L

The completely sweetened oil leaving separating tank 2 through line I8 may passdirectly to storage, not shown, or to subsequent steps wherein the lstock may be treated with an alkaline suliide solution, as described in U. S. -1,980,555 to render it stable toward formationof deleterious compounds.

Considering further our invention from ythe view point of the most eicient utilization of the oxidizing power or oxidation potential of f the treating solution, the process sums upto be essentially a =twostagetreating process using a single contacting pump.- Souroil entering through line 3 contacts in contacter 6V partially spent treating solution. Following this step, partiallly sweetened oil then contacts` regenerated treating. solution in mixer -`I. In further explanation, :the fully regenerated treating solution entering through line II may have an oxidationvpotential as high as 420 millivolts, upon passing through the cen= trifugal mixer I, -this potential may be reduced'to,

say, 390 m.-v., this partially spent solution then separates from the sweetened oil in separator 2, and passes by line I3 to line 3 to contactor 6, wherein the oxidation potential may drop -to as low as, say, 360 m. V., and in this condition the solution is generally considered fully spent. In contactor`6 the easy-tof-sweeten mercaptans have been oxidized by the above said partially spent treating solution of, say, 390 m; v., while those not so sweetened but areslower and more dinicult to sweeten are treated by the fully regener-v ated copper solution of, say, 420 rn. v. in the centrifugal contactor I, lthus giving in effect the above said two-stage contacting.

In contrast to this herein disclosed countercur rent two-stage operation, in conventional practice the regenerated copper treating solution of, say, 420 millivolts, contacts the sour oil wherein the high oxidation potential expends itself in sweetening the mercaptans which are easiest to sweeten. The resulting treating solution, partially spent and possessing a much lowered oxidation potential, then must react withthe veryslow-to-react mercaptans, and for this reason contacting times are materially increased in certain rather exceptional cases.

In case the oil contains mercaptans which are extremely refractory toward-sweetening, the valve 22 in bypass line 2I may be opened to permit bypassing or recycling of an amount of the copper treatings'olution'and the treatedoil. The by .passed oil mixeswith the sour oil in line 3 while the bypassed partially spent .treating solution mixes `in line 3 with the treating solution from line I3.' In thisvmanner the theoretical oil retention and'therefore contacting time in the system is increased in proportion to the amount of oil bypassed. As stated above, primary mercaptans react rapidly with the cupric chloride solution while the tertiary mercaptans react relatively slowly, and the latter is especially true in case of high molecular weight tertiary mercaptans'. In

the chemical oxidation reaction between, for ex-v ample, butyl mercaptan and cupric chloride, dibutyl disulfide is vformed, and secondary amyl mercaptan should yield the corresponding diamyl disulfide. In like marinera tertiary mercaptan shouldV yield the corresponding di (tertiary) disulfide,v and' it is this latter type of mercaptans orl a hexyl-secondary or tertiary amyl disulfide.

These mixed disulfldes may be formed in accordance with the law of probabilities,` and a mixed disulfide, for example', primary butyl-tertiary amyl disulfide should -beformed from its v constituents more easily thanwill di (tertiary) amyl disulfide. It is known in practice that the addition of a. small proportion-,of a primary mer,-

. captan assists in the sweetening of an oil'which is rvery difficult or slow to sweeten, and the above explanation is given in an attempt to explain this known` fact. And it is also lmown that a'trace of sourness appearing in the oil dischargedfrom the mixing pump I usually disappears upon opening of the bypass valve 22 permitting recycling to occur. Essentially any proportion of the mixing pump` discharge may be recycled, as say from 10 to as highas 50-60% by volume; Upon recycling as much as this 50% materially increases the retention time of the oil in the treatingr system.

Example Three thousand `barrels per day of` gasoline generally considered difficult to sweeten, equivalent to barrels per hour, were treated in a plant of design illustrated in the accompanying drawing. 'I'he mixture of gasoline and treating solution passing valve I'I, was composed of 60 volume percent of gasoline to 40 volume percent of treating solution. The regenerated copper solution added throughline II possessed an oxidation.potential of 410 mllivolts. vAfter thorough contacting in the centrifugal mixing pump I, the treating solution taken from .sampler I4 had dropped to a potential of 390`millivolts, a decrease of 20 m. v. Upon settling out the treating solution in tank 2, the treated gasoline was fully sweet to the-standard doctor test. The settled treating solution of 390 millivolts was then passed l to the contacting column 6 in which contact was made with the sour charge stock, the potential of the treating solution herein being reduced to 360 millivolts; This fully spent solution was separated from the partially sweetened gasoline in separatingtank 8 and sent to a regeneration unit.

The size or capacity o1 separator tank 2 was such that the gasoline therein had a retention or settling time of 5 minutes. Tank, havingthe same volumetric capacity as separator tank '2,

and carrying the copper solution level corre-v f spondingly as high'in tank 8 as it is carried low intaniez, gave:theecopperfsolutioxra-settlingrtime ofi '121/2 minutes, whic'hawass ampletor free' the-.copnerfsolutionoroil.

The retention time: of theitreating 'solutioxrrin separatingftank lfwas-veryrshort; being approximately 1/2 minute', thusy asffthis solution ,was withdrawnthroughline I3it wasV not entirely'free of sweetened gasoline,` ,having retained therein.` 2 `or 3 volume percent gasoline- Itwwas found.l that this carry back or gasoline waslnot detrimental to the process in any way,v andinzfact was'equivaF lent to the recycling ofthe gasolinevtreating solutionmixturethrough line12l, but, ofcourse, to a lesser'extent; V

Similarly; the very short reteni'liorrtime` of. the gasoline'in tank 8did notA permit: complete; settling of all the treatingsolutionr and 3cr 4; volumeperL centl of-the spent 'treating' solution was; carried from tank to mixing pump I'with the partially sweetened gasoline.v This carry'o'er of spent treating solution lowered .the oxidation. potential of the regenerated` treating f solution added throughline Il byf2=tol3 millivolts,4 which drop was considered negligible.

TheV oxidationV potential values given herein. are given merely, in explanation` of the operation of the, process, andare not intended tobe a-limiting factor in any manner. The oxidation: potential drop 'upon` contact Withzthe sour oil'is dependent 1 uponseveral factors; forexample, the sourness of the oil,- the ratio of sour:4 oiltotreating solution as well asuponother factorsfofilesser importance. The extent towhich regeneration of the spent treating solution is carried is; dependent upon such. factors :as plant; design, sourness of the-oil to be sweetened,` and the relative ease with which the oil can be sweetened,.in general, the-more'dicult the oil Vto sweetenthe higher the oxidation potential shouldbe carried;

It will be understoodthat'suitable corrosionresistant materials offconstruction are used in constructing the apparatus shown inthe-drawing.

It will alsobe understood by one skilledin the art that points: ofv design, tank. sizes; andmany other variable points. may beraltered Within rather wide limits and yet remain within the intended scope and spirit of our invention.`

whatwe-fclaimis:

1. Thev process of sweetening a sour hydrocarbon clin which at leasta; portionv ofthe sourness is slow to sweetenwhich comprises introducing said sour oil into-an extended'flowingvand treating zone, separately introducing an aqueous copper treating solution to said zone intoI admixture with said oil, passing said mixture along said zone wherein agitation of the mixture occurs to-pro ducecontactbetween the-oil phase and the aquecus phase vwherein a portion ofthe sourness is aarsgoea sweetened; passing-.the-partially.sweetenedaoiland copperf treatinglsolution: mixture .tova separating and an upper layer of sweetened oil, and remov-V ing said sweetened oil; recycling said second lower layer of copper treating solution as'the rst mentioned aqueous copper treating` solution.

2; The'process of sweetening a sour hydrocarbon oil in which atleast ay portion ofthe sournessis slow to sweeten which comprisesintroducing. said sour oil into an extended flowing and treating zone, separately introducing a partially spentaqueousY topper'I treating solution to said zone intoiadmixture with said oil, passing'said admixture along said zone wherein agitation of the mixture occurs to produce contactI between theL oil phase and the aqueous phase wherein a portion; ofthe sourness is sweetened and-thepartially spent copper treating solution becomes spent;` passing the partially sweetened oil and spent copper'tr'eating solution mixture toa. sepa'- rating-zone, separating this mixtureinto a, lower layer of spent copper treating solution and an upper layerof partially-sweetened oil, and removing; the said` spent coppeitreating` solution; passing the partially sweetened oil into a second contacting zone, separately introducing regenerated copper'treating solution to saidsecond contacting zoney into :adn'iixtureY with the partially-sweetened oil; vigorouslyagitatingsaid admixture-to eirect sweetening-of'the sourness slow to sweeten and wherein the regenerated treating solution Lbecomes 'partially spent, passing this latter resulting mixture to a .secondseparating zone, separating this mixture into a partiallyfspent copper treating so"- lution layer and a layer'of sweetened oil, and-'re` moving said sweetened oil; recycling'said partially spentacopperr treating solution as 1the rst mentionedpartially spent copper treating solution 3 Same as claim 2, in which a portion ofthe latter resulting mixture passed to the second separating zone is bypassed from the said second separating Zone into the extended owing and treating zone.

H. E. MESSMORE.

Jl M. MASON. 

